simplify (and document!) macro for inlinable API functions (inspired by bug #4603, with slightly different implementation)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@6090 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/inline_api.h

@@ -0,0 +1,57 @@
+/*
+ * Asterisk -- A telephony toolkit for Linux.
+ *
+ * Inlinable API function macro
+ *
+ * Copyright (C) 2005, Digium, Inc.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License
+ */
+
+#ifndef __ASTERISK_INLINEAPI_H
+#define __ASTERISK_INLINEAPI_H
+
+/*
+  Small API functions that are candidates for inlining need to be specially
+  declared and defined, to ensure that the 'right thing' always happens.
+  For example:
+  	- there must _always_ be a non-inlined version of the function
+	available for modules compiled out of the tree to link to
+	- references to a function that cannot be inlined (for any
+	reason that the compiler deems proper) must devolve into an
+	'extern' reference, instead of 'static', so that multiple
+	copies of the function body are not built in different modules
+	- when LOW_MEMORY is defined, inlining should be disabled
+	completely, even if the compiler is configured to support it
+
+  The AST_INLINE_API macro allows this to happen automatically, when
+  used to define your function. Proper usage is as follows:
+  - define your function one place, in a header file, using the macro
+  to wrap the function (see strings.h or time.h for examples)
+  - choose a module to 'host' the function body for non-inline
+  usages, and in that module _only_, define AST_API_MODULE before
+  including the header file
+ */
+
+#if !defined(LOW_MEMORY)
+
+#if !defined(AST_API_MODULE)
+#define AST_INLINE_API(hdr, body) hdr; extern inline hdr body
+#else
+#define AST_INLINE_API(hdr, body) hdr; hdr body
+#endif
+
+#else /* defined(LOW_MEMORY) */
+
+#if !defined(AST_API_MODULE)
+#define AST_INLINE_API(hdr, body) hdr;
+#else
+#define AST_INLINE_API(hdr, body) hdr; hdr body
+#endif
+
+#endif
+
+#undef AST_API_MODULE
+
+#endif /* __ASTERISK_INLINEAPI_H */